1. Field of the Invention
The present invention relates to a multistage plant culture method adapted to grow plants such as Cucurbitaceae, Solanaceae, Rosaceae, and the like for fruit harvest, and a multistage plant culture apparatus for use in such a multistage plant culture method.
2. Description of the Related Arts
Culture in greenhouses of fruit vegetables such as eggplants, tomatoes, cucumbers, melons and the like and fruit trees has recently been carried out extensively. In such culture methods, seedlings are planted in soil in open culture or in culture beds such as culture containers filled with rooting media of rock wool slab or the like. In the culture of fruit vegetables using culture beds, seedlings are planted in such culture beds placed on the ground and are allowed to grow upwards, and, in order to achieve as high a yield as possible, fruit is harvested after fruiting from multistage flower clusters. For example, tomato plants are usually grown to bear fruit up to the fifth or sixth flower cluster before harvest.
In such tomato plant culture, i.e. up to the fifth or sixth flower cluster, two crops a year are possible in general. From planting to the end of harvesting represents one cycle and after the first crop, a certain resting period (one week to one month) is taken for clearing out the remaining plants, sterilizing the culture beds and the like before commencing the second crop. Even if the resting period is made as short as possible and the seedlings of the second crop are planted immediately after the first crop has finished (so as to grow the plants up to the highest possible flower cluster) only two crops a year up to the seventh or eighth flower cluster are possible. Moreover, the commencement of harvesting the fruit is usually around the flowering time of the fifth flower cluster and hence the period from planting to the harvesting of the first fruit represents a lost period in which no fruit can be harvested.
Accordingly, in such a conventional culture method, there is a long lost period from planting to the start of harvest, and the harvesting period is restricted. Hence, a culture method capable of allowing a continuous harvest extending over a long period has been sought.
In order to meet this demand, a method for growing plants up to a higher multistage flower cluster has been developed; and although an initial lost period still exists in this method, plants can be continuously grown up to more than the thirtieth flower cluster stage. However, since the growth of stems and leaves occurs simultaneously with flowering, fruiting and thickening, there is required a supply of nutrient solution which maitains a balance between vegetative growth and reproductive growth. It is quite difficult to effect such a nutrient solution supply and its success largely depends on the technical skill of the growers. Hence, such a high multistage culture method is too labour intensive and is thus not suited to automation of the nutrient solution supply and large scale culture.
French Patent No. 1,491,459 discloses a method for growing up plants on a plurality of stages at different heights, the growing plants being in order moved from the upper stages down to the lower stages. However, in this conventional method, concerning a timing of plant moving, only the following description appears, that is, different predetermined periods depending on varieties of plants to be cultivated and predetermined amounts of daily solar radiation required for flowerings are used as criteria. Hence, in the end, a judgement of whether or not the timing of plant moving has come, in other words, whether or not the plant has received a sufficient amount of daily solar radiation required on a certain stage is carried out by worker's subjectivity. This conventional method is thus not suited to automation of the culture work and large scale culture.